JP4585904B2 - Color misregistration correction method and image forming apparatus - Google Patents

Description

  The present invention relates to a color misregistration correction method for detecting and correcting a color misregistration amount, and a color image forming apparatus such as a copying machine, a printer, a facsimile, a digital multi-function peripheral, etc. that implements the color misregistration correction method.

  2. Description of the Related Art Today, electrophotographic apparatuses are increasing in color output such as color copiers and color printers in response to market demands. Particularly recently, since monochrome speeds are desired for color output, a plurality of photoconductors and individual developing devices are provided, and a single color toner image is formed on each photoconductor, and those single color toner images are sequentially formed. Tandem printers that transfer and record color images on recording paper have become mainstream.

  In the tandem printer, as shown in FIG. 12, images formed on the photoreceptors 2K, 2M, 2C, and 2Y (K, M, C, and Y indicate colors) provided for each color are displayed. Full-color images are obtained by developing toner with the developing units 3K, 3M, 3C, and 3Y, and sequentially transferring onto the recording paper conveyed by the transfer belt 51 by the transfer devices 4K, 4M, 4C, and 4Y provided for each color. As shown in FIG. 13, the images formed on the photosensitive members 2K, 2M, 2C, and 2Y are temporarily transferred onto the transfer belt 51 by the transfer devices 4K, 4M, 4C, and 4Y. There is an indirect transfer type that sequentially transfers and transfers a full color image formed on the transfer belt 51 onto a recording sheet by a secondary transfer device 54. We shall take a configuration using a belt often. In any of the methods, the images on the photosensitive members 2K, 2M, 2C, and 2Y of the respective colors are transferred onto the recording paper or the belt at different positions on the transfer belt 51, so that the moving speed of the transfer belt 51 is very small. When there is a change, the arrival time to the next color transfer position varies. Due to this variation, a shift occurs in the transfer position of each color, resulting in a color shift in the sub-scanning direction (belt moving direction) in the output image. In addition, since the writing units 1K, 1M, 1C, and 1Y are also independent for each color, the magnification in the main scanning direction and the writing position change due to displacement of each component due to environmental changes such as temperature. As a result, a color shift in the main scanning direction occurs in the output image.

  For this reason, the tandem printer outputs a toner pattern for detecting misregistration as shown in FIG. 14 on the transfer belt 51 before forming an actual color image, as disclosed in Japanese Patent Application Laid-Open No. H10-228707. Detecting this pattern with a sensor, calculating the amount of deviation or correction from the normal position of each color from the detection results, and adjusting the image writing timing and magnification based on the amount of correction Many have a function to correct.

  12 and 13, reference numeral 6 denotes a fixing unit, reference numeral 7 denotes a plotter control unit, reference numeral 52 denotes a driving roller, and reference numeral 53 denotes a driven roller.

Furthermore, in Patent Document 2, engine calibration is performed with minimum execution frequency with minimum downtime, and the result is reflected in the next print so as to maintain the image quality while reducing the waiting time of the user. An image forming apparatus is disclosed.
JP 2002-244387 A JP 2003-167394 A

  However, the amount of color misregistration greatly depends on the usage situation and installation environment. The cause of color misregistration is greatly affected by temperature changes inside the machine. However, when a large number of sheets are printed continuously and when a small amount is printed at time intervals, the set number of sheets is reached. Since the temperature state inside the machine at the time is different, the amount of color shift is also different. For this reason, even if the color misregistration correction is performed for every fixed number of sheets, a large difference occurs in the misregistration amount before the color misregistration correction, and it is difficult to set an optimum condition.

  Therefore, if color misregistration correction is executed every time printing is started and then printing is started, the amount of color misregistration at the start of printing can be kept within a predetermined range. Since the time becomes longer, the user-friendliness becomes worse. In addition, when a certain number of sheets are printed during continuous printing, the color misregistration amount can be reduced by setting the value to reduce the value of the certain number of sheets when performing color misregistration correction and shortening the color misregistration correction execution interval. Although it can be kept in a good state, since the number of times of color misregistration correction during printing increases, the throughput deteriorates and user convenience deteriorates.

  The present invention has been made in view of such a state of the art, and an object of the present invention is to prevent occurrence of color misregistration that lowers the quality of a formed image without lowering the throughput. .

In order to achieve the object, the first means outputs a toner pattern for detecting a color misregistration amount on the belt, detects the position of the toner pattern, and detects the color misregistration amount from the detected toner pattern position information. In the color misregistration correction method for calculating the color misregistration amount so as to minimize the color misregistration amount, the time interval from the previous printing end time to the current printing start time is measured, and is executed after the measuring step. Obtained based on the set execution condition, the step of determining whether or not a large amount of printing is continuously performed, the step of setting the execution condition for executing the next color misregistration correction according to the measured execution interval. number of prints and the step of comparing the predetermined number, and a step of performing the color misregistration correction processing when the number of printed sheets in the step of the comparison is greater than the predetermined number, the step of determining After When it is determined that continuously are printed in large quantities is subjected to the color shift correction, and executes a process for setting the execution condition.
The second means calculates the color misregistration amount from the means for outputting a toner pattern for detecting the color misregistration amount on the belt, the means for detecting the position of the toner pattern, and the positional information of the detected toner pattern. In the image forming apparatus having the means for correcting so that the color misregistration amount becomes the minimum, the means for measuring the time interval from the end time of the previous printing to the start time of the current printing is executed after the measuring step. Obtained based on the set execution condition, means for determining whether or not a large amount of printing is continuously performed, means for setting an execution condition for executing the next color misregistration correction according to the measured execution interval. Means for comparing the number of printed sheets with a predetermined number of sheets, and means for executing a color misregistration correction process when the number of printed sheets is larger than the predetermined number of sheets as a result of comparison by the comparing means. After when said determining means are mass printed in succession subjected to the color misregistration correction, and sets the execution conditions.
In this case, when the number of prints from the previous color misregistration correction is calculated, the setting means multiplies the number of prints by a constant coefficient according to the interval until the next print. An execution condition is set in which the number of printed sheets is less than the actual number of printed sheets. In addition, the apparatus further includes means for measuring the environmental temperature, and the means for setting changes a coefficient indicating a change in color misregistration due to the standing time according to the measured environmental temperature, and performs an optimal correction according to the change in the coefficient. It is also possible to set an execution condition for executing the next color misregistration correction using the coefficient. The belt may be, for example, a conveyance belt that conveys a sheet on which an image is directly transferred, or an intermediate transfer belt on which an image is primarily transferred and the transferred image is transferred onto a sheet at a secondary transfer position. Is used.

  In the embodiment described later, the process of measuring the execution interval of the printing process is performed in steps B16 to B3, the process of setting the execution condition is performed in step B4, and the process of comparing is performed in steps B5 and B12. The process of executing the process corresponds to steps B6, B13 and C3, and the process of determining whether or not a large amount of printing is performed continuously corresponds to step C2.

  Further, the means for outputting the toner pattern is applied to the entire image forming element formed via the plotter control unit 7 in accordance with an instruction from the CPU 100, the means for detecting the position is applied to the toner mark sensor 108 and the CPU 100, the correcting means, and the measurement. The means for performing and the means for setting correspond to the CPU 100, and the means for measuring correspond to the temperature detection sensor 109, respectively.

  According to the present invention, since the execution condition for executing the next color misregistration correction is set according to the measured execution interval of the printing process, the color that reduces the quality of the formed image without reducing the throughput. The occurrence of deviation can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. In the figure, an image forming apparatus according to the present embodiment includes a CPU 100, a ROM 101, a RAM 102, a parameter memory 103, a time measuring unit 104, an operation display unit 105, a plotter 106, an I / O unit 107, a toner mark sensor 108, and a temperature detection. It basically includes a sensor 109, a motor control unit 110, a motor driver circuit 111, a motor 112, and a system bus 113.

  The CPU 100 is a central processing unit that executes a program written in the ROM 101 and controls each part of the apparatus. The ROM 101 is a read only memory in which a program for the CPU 100 to control each part of the apparatus and fixed data used for control are stored. A RAM 102 is a random access memory used to develop a work area when the CPU 100 executes a program for controlling each part of the apparatus and an image to be printed. The parameter memory 103 is a non-volatile memory for storing data related to the operation of the apparatus even when the power is shut down and for storing data that is referred to at the next operation, and is a battery-backed SRAM or EEPROM. Consists of. The parameter memory 103 stores data that is updated when color misregistration correction is performed, such as a color misregistration correction execution interval, a color misregistration correction pattern parameter, and a color misregistration correction amount.

  The time measurement unit 104 uses an internal clock of the system, and measures the elapsed time since the color misregistration correction processing is executed by counting the clock. It has a clock function for measuring time, and measures the time when color misregistration correction processing is performed. In addition, an elapsed time from when color misregistration correction is performed can be calculated from a difference from the current time. The operation display unit 105 includes operation keys for the user to set the device and the like, and a display unit such as a liquid crystal display for displaying the operation state and message of the device to the user.

  The plotter 106 is a part that performs an operation of forming and outputting an image on a recording paper 70 (see FIG. 2), and is controlled by the plotter control unit 7. A detailed configuration of the plotter 106 is shown in FIG. The I / O unit 107 includes an input / output port, and controls input and output of the toner mark sensor 108 and other sensors. The toner mark sensor 108 is a sensor that detects a toner mark generated on the transfer belt 51. When the optical sensor is used, the transfer belt 51 is irradiated with light, a toner mark for measuring the color misregistration amount generated on the transfer belt 51 is detected, and information for measuring the color misregistration amount is obtained. . An example of the toner mark is as shown in FIG. The temperature detection sensor 109 is a sensor for detecting the environmental temperature, and detects the ambient temperature where the image forming apparatus is installed using a temperature sensor such as a thermistor. The motor 112 is a motor that drives each part of the image forming apparatus according to the present embodiment, and is controlled by a drive signal supplied from the motor control circuit 110 via the motor drive circuit 111. The system bus 113 is a signal line for the above-described units to exchange data. Specifically, the system bus 113 is configured as a set of a data bus, an address bus, a control bus, and an I / O bus.

  FIG. 2 is a diagram showing a schematic configuration of the plotter unit 106. In the figure, a plotter 106 is of an electrophotographic tandem type, and four drum-shaped photoconductors 2K, 2M, 2C, and 2Y and images formed on the photoconductors 2K, 2M, 2C, and 2Y are displayed. It comprises a belt-like transport device (transfer belt 51) that transports the recording paper 70 so as to be sequentially transferred onto the recording paper 70 at the transfer positions of the respective transfer devices 4K, 4M, 4C, 4Y provided for each color. This is a direct transfer type configuration and corresponds to FIG.

  In the image forming apparatus configured as shown in FIG. 2, the image data is first decomposed into image data of cyan (C), magenta (M), yellow (Y), and black (K) by the plotter control unit 7. Are converted into data for each color for writing. The photosensitive drums 2K, 2M, 2C, and 2Y are exposed to the laser light output from the writing units 1K, 1M, 1C, and 1Y, and the photosensitive layers on the photosensitive drums 2K, 2M, 2C, and 2Y correspond to the image data. An electrostatic latent image is formed. The electrostatic latent images formed on the photosensitive drums 2K, 2M, 2C, and 2Y are developed by the developing devices 3K, 3M, 3C, and 3Y corresponding to the respective colors, and become toner images of the respective colors. The developed toner image is fed from the paper feed cassette 71 and sequentially transferred onto the recording paper 70 supplied to the transfer unit 4, and four colors are superimposed on the recording paper 70 to form a color image.

  The transfer unit 4 includes transfer belts 51 that are in contact with the photosensitive drums 2K, 2M, 2C, and 2Y of the respective colors and transfer devices (transfer roller units) 4K, 4M, 4C, and 4Y that are opposed to the photosensitive drums 2K, 2M, 2C, and 2Y. Consists of. The recording paper 70 is conveyed in an electrostatically attracted state on the transfer belt 51, and the toner image is transferred to the recording paper 70 at the position where it contacts the photosensitive drums 2 K, 2 M, 2 C, and 2 Y.

  The transfer belt 51 is an endless belt, is stretched between the driving roller 52 and the driven roller 53, and is driven to operate at a constant speed by a motor 112 connected to the shaft of the driving roller 52. A cleaning device 54 is installed on the downstream side of the driving roller 52 in the rotation direction of the transfer belt 51 to clean an unnecessary toner image on the surface of the transfer belt 51. As the transfer belt 51, for example, a belt in which all layers of the belt are formed of fluorine-based resin, polycarbonate resin, polyimide resin, or a part of the belt is used. A fixing unit 6 is provided on the downstream side of the transfer belt 51 in the conveyance direction. In the fixing unit 6, the recording paper 70 to which the toner images of the respective colors are transferred is fixed on the recording paper 70 by heating and pressurizing and output.

  In this embodiment, the direct transfer type printer has been described. However, the present invention can be similarly applied to an indirect transfer type printer as shown in FIG.

  In the image forming apparatus configured as described above, the following color misregistration correction processing is performed.

  In the color misregistration correction process, as shown in FIG. 14 described above, four strip-shaped toner patterns 11K, 11M, 11C, and 11Y having different colors formed on both sides in the main scanning direction on the transfer belt 51 are marked with toner marks. The detection is performed by the sensor 108, the color misregistration amount between the patterns 11K, 11M, 11C, and 11Y of the respective colors is detected, and the writing timing is adjusted so that the color misregistration amount becomes a predetermined value or less. Is called.

 In the direct transfer method shown in FIG. 10, the toner patterns 11K, 11M, 11C, and 11Y are indirect transfer shown in FIG. 11 at a position facing the nearest position on the downstream side in the rotation direction of the transfer belt 51 of the drive roller 52. In the system, the drive roller 52 is formed at a position facing the nearest position on the upstream side in the rotation direction of the transfer belt 51. The patterns 11K, 11M, 11C, and 11Y are formed of a series of strip-like patterns in accordance with the arrangement of the toner mark sensor 108, and in the same manner as normal image formation at a plurality of locations in the main scanning direction, the photosensitive drums 2K, 2M, 2C, and 11Y. It is formed by transferring from 2Y. In this embodiment, although it arrange | positions in two places, it is good also as a structure which arrange | positions a pattern three or more places according to the number of sensors. The pattern itself is visualized by the CPU 100 by reading the parameter data of the pattern stored in the parameter memory 103 from the plotter control unit 7 through the above-described steps.

  In any case, at the time of color misregistration correction, the recording paper 70 is not passed, and the toner pattern for misregistration detection shown in FIG. 14 is output on the transfer belt 51, and this pattern is detected by the toner mark sensor 108. From the detection result, the CPU 100 detects and corrects the amount of deviation of each color from the normal position. Each pattern is composed of four parallel linear patterns 11-1 and four diagonal line patterns 11-2, and a pair of these line patterns 11-1 and 11-2 is sub-scanned as a pair. These are arranged at regular intervals in the direction, and a plurality of sets thereof are repeated and formed along the moving direction of the transfer belt 51. In this embodiment, four colors of yellow (Y), cyan (C), magenta (M), and black (K) are formed.

  Each part not specifically described is configured in the same manner as the direct transfer type printer shown in FIG. 12 and functions in the same way.

FIG. 3 is a flowchart showing a processing procedure of color misregistration correction processing using this toner pattern, and is executed by the CPU 100.
In this processing procedure, when processing is started (step A1), a toner pattern for detecting the amount of color misregistration between colors is output as a pattern output prior to normal image output (step A2). The toner pattern is formed on the transfer belt 51 via the photosensitive drums 2K, 2M, 2C, and 2Y, and is the pattern shown in FIG. Next, the toner patterns 11K, 11M, 11C, and 11Y for color misregistration detection formed on the transfer belt 51 are detected by the toner mark sensor 108, and the detected waveform is binarized and the falling edge and the rising edge are detected. The position of the middle point is detected as position information of each line pattern (step A3).

  Next, a deviation amount in the main scanning direction and a deviation amount ΔD in the sub-scanning direction are calculated from the position information of each line pattern detected in step A3. Then, a correction amount that minimizes the shift between the colors is calculated from the calculated shift amount ΔD. The calculated shift amount and correction amount are stored in the parameter memory 103 and used as correction values until the next color shift correction process (step A4). Next, using the correction amount calculated in step A4, main-scan and sub-scan resist correction is performed. Further, the magnification and the magnification error deviation are corrected (step A5).

  Step A5 After the color misregistration correction is performed, the color misregistration detection pattern is output again in a state in which the correction result of the color misregistration correction process is reflected, and the pattern after the color misregistration correction is formed on the transfer belt 51 (Step S5). A6). The uncorrected toner pattern 11 first formed on the transfer belt 51 is removed by the cleaning device 54 after detection by the toner mark sensor 108.

  The color misregistration detection pattern on the transfer belt 51 after the color misregistration correction output in step A6 is detected again by the toner mark sensor 108, and each position information of the line pattern 11 is detected (step A7). Next, from the detected edge information of each line pattern 11, the skew, the amount of deviation in the main scanning direction, and the amount of deviation in the sub-scanning direction are calculated similarly to the previous time, and the correction amount that minimizes the deviation between these colors is calculated. Calculate (step A8).

  When the correction amount that minimizes the shift between the colors is calculated in step A8, it is determined whether the color shift amount between the patterns after the color shift correction is smaller than a predetermined value (Δd) (step S8). A9) If it is smaller than Δd (Yes determination), the process is terminated (step A10). On the other hand, if it is larger than Δd (No determination), the process returns to Step A5, the correction amount is calculated again from the detected position information, and the processes after Step A5 are repeated.

  By performing such a series of processes, the color misregistration amount between the colors can be adjusted to a value smaller than a predetermined value (Δd).

  In this example, the color misregistration correction process is performed once, and the color misregistration detection pattern is output again with the correction result reflected to reduce the color misregistration amount to a predetermined value or less. When giving priority, it is good also as operation | movement which complete | finishes by the process to step A4.

  By performing the color misregistration correction process using the color misregistration correction function in this manner, the color misregistration amount can be kept within a predetermined range. However, the number of prints and the time interval between printing and printing depend on the use environment. Because of the difference, the method of managing the color misregistration correction execution interval only by the number of images cannot keep the image quality constant, and if the execution interval is short, the processing efficiency decreases and the execution interval is long. In many cases, the amount of color misregistration increases. Therefore, in this embodiment, the time measurement unit 104 measures the execution interval of the printing process, and the execution condition for executing the next color misregistration correction is adjusted according to the execution interval of the printing process. Specifically, when adding up the number of prints from the previous color misregistration correction, multiply the number of prints by a certain factor according to the interval until the next print. Less than the number of prints, it is difficult to reach the preset number of color misregistration corrections, and sufficient image quality can be obtained even if the frequency of color misregistration correction is reduced. I was able to.

  The processing procedure at this time is shown in the flowchart of FIG. When the process shown in FIG. 4 is started (step B1), a print request standby state is entered at step B2. In step B2, it is determined whether or not a print request has been issued. If no print request has been issued, the process stands by. When a print request is issued, the elapsed time from the previous print end time is measured in step B3. In the time measurement, the time measurement counter in the time measurement unit 104 is cleared and the count is started in step B16, so that the elapsed time can be calculated by reading the counter value in step B3. The time measuring unit 104 used here measures the elapsed time from the end of the printing process by counting the clocks in the system.

  After measuring time in step B3, the process of step B4 is executed. The process of step B4 is a process of calculating the number of prints from the previous color misregistration correction, but the number of prints is the same as the number of prints P immediately before the previous print from the previous color misregistration correction. A value obtained by multiplying the number of printed sheets P1 at the time of printing by a certain coefficient is added. The coefficient used here is obtained using the table shown in FIG. 6 using the elapsed time calculated in step B3. Since the temperature change at the time of the printing process and when left after the printing process is as shown in FIG. 5, there is a high possibility that the color shift also takes the same change. That is, even if the temperature rises during printing and the color misregistration deteriorates to some extent, the amount of color misregistration returns to its original value as time passes and approaches the initial state. However, color misregistration is caused by factors other than temperature, and is not completely restored. Therefore, even when a sufficient amount of time has passed, the table has a certain amount of ratio instead of zero. The conversion table shown in FIG. 6 is merely an example, and an actual machine prepares and uses a conversion table that matches the characteristics of the device.

  In step B5, the number of printed sheets P obtained from the previous color misregistration correction obtained in step B4 is compared with a preset number of sheets that serves as an execution standard for color misregistration correction. If P exceeds the set number, Then, color misregistration correction processing is executed (step B6). In the color misregistration correction process in step B6, as described above, a color misregistration detection pattern is formed on the transfer belt 51 with toner, and this pattern is detected by the toner mark sensor 108, whereby the main scanning direction and the sub scanning direction are detected. This process adjusts the resist and magnification to minimize the color misregistration of the four colors. The shift amount and correction amount calculated here are stored in the parameter memory 103 so that they can be used as correction values until the next color shift correction process. Next, in step B7, the number P of prints since the previous color misregistration correction and P1 counting the current print processing are each cleared to zero.

  In step B5, if the number P of prints since the previous color misregistration correction is equal to or smaller than the preset number of prints that is the execution standard for color misregistration correction, normal printing processing is executed (step B9). During the printing process, it is necessary to count the number of printing processes this time, so the counter P1 is cleared in step B8 and counted in step B10. In addition, during printing execution, there may be a case where the set number of sheets serving as a reference for executing color misregistration correction is exceeded. Therefore, in step B11, the current number of prints P is set to the previous printing from the previous color misregistration correction. The value obtained by adding the number of printed sheets P1 is counted as P2, and if the value of P2 exceeds the set number in step B12, color misregistration correction processing is executed in the same manner as in step B6 (step B13), and in step B14. The number of printed sheets P from the previous color misregistration correction is cleared to zero. Also, P1 counting the current printing process is cleared to zero.

  In step B15, it is determined whether or not the output image is the last page. If it is not the last page, the process returns to step B9 to output the image again. If it is determined in step B15 that the page is the last page, the process proceeds to step B16. In step B16, since the time from the current printing process to the next printing process is measured, the time measurement counter in the time measurement unit 104 is cleared, the count is started, and the process returns to step B2 in this state. Wait for the next print request.

  Through the series of processes described above, the number of output sheets for determining color misregistration correction during execution of printing can be implemented using a value obtained by changing the printing interval with time.

  In this way, when the set number of sheets for executing the color misregistration correction process is 100 pages, when printing for every 20 pages is repeated at intervals of 20 minutes, in the conventional process, the color is printed once every 5 times. In the control according to the present embodiment, the deviation correction processing is executed once in 10 printings. Thereby, it is possible to adjust the execution interval according to the usage status of the user.

  In the present embodiment, the time measuring unit 104 is configured to use a time measuring counter, but may be configured to use a real-time clock. The real-time clock is an IC dedicated to timekeeping, and the current time information can be acquired by reading it from the system using a command. Since the real-time clock operates with very low power consumption, it can continue to operate by receiving power supply while the system is powered off by backing up with a battery.

  In this embodiment, when the printing interval is long, the internal state of the machine returns to the steady state, and thus the color shift caused by the temperature change also returns to the initial state. Therefore, even if the number of printed sheets is less than the actual number of printed sheets and integrated, the amount of color misregistration can be kept within a certain range. However, since the time required for the internal state of the machine to return to the steady state varies depending on the installation environment, a large difference occurs in the amount of deviation before color misregistration correction when controlled at a constant ratio with respect to the elapsed time. Sometimes. Therefore, measure the environmental temperature, change the coefficient indicating the change in color misregistration depending on the ambient temperature, and adjust the execution condition to execute the next color misregistration correction using the optimal correction coefficient. You can also That is, the correction coefficient is changed in accordance with the environmental temperature of the image forming apparatus, and the execution interval of the color misregistration correction process is optimized.

  Moreover, although the coefficient used for this embodiment is calculated | required using one type of table shown in FIG. 6 using the elapsed time calculated by step B3, when environmental temperature differs, as shown in FIG. In some cases, the inclination at which the temperature at the time of leaving is restored differs greatly. Therefore, the ambient temperature is detected using the temperature sensor 109, and an optimum one is selected from the correction coefficients in the table shown in FIG. 8 according to the detected value. The temperature detection sensor 109 is a sensor for detecting the environmental temperature, and detects the ambient temperature where the image forming apparatus is installed using a temperature sensor such as a thermistor. Color misregistration is caused by factors other than temperature, so it is not completely restored. Therefore, even when a sufficient time has elapsed, the table having a certain amount of ratio instead of 0 is the same as the case of the table of FIG. Naturally, the conversion table shown in FIG. 8 shows an example when a plurality of correction coefficients are set, and the actual machine prepares and uses a conversion table that matches the characteristics of the device.

  As described above, according to the present embodiment, the time of the printing process execution interval is measured, and the timing for executing the next color misregistration correction is changed according to the printing process execution interval. In the case of a usage pattern in which printing is performed at intervals, it is possible to lengthen the execution interval as compared with a case where color misregistration correction processing is simply performed for each fixed number of pages. In addition, when a large amount of printing is continuously performed, the color misregistration correction process is performed with a predetermined number of sheets, so that the color misregistration amount can be always kept within a certain range. For this reason, it is possible to perform color misregistration correction processing at an optimal interval according to the usage pattern.

  Furthermore, since the execution interval until the next color misregistration correction is performed according to the environmental change, the color misregistration amount can be controlled to be always within a certain range with high accuracy.

<Second Embodiment>
In the first embodiment, by performing color misregistration correction at regular intervals, the amount of color misregistration can be kept within a predetermined range during continuous printing. However, the color misregistration amount changes depending on the elapsed time from the color misregistration correction process to the next printing due to the influence of the temperature change. In particular, when correction is performed during continuous printing and then left unattended, the color misregistration is corrected in a state where the temperature has risen, so that the correction is made to be far away from the initial state. For this reason, when the printer is left in this state and returned to the initial state, printing is performed using the setting value in a state of being largely separated, and the amount of color misregistration may increase at the start of the next printing. .

  Therefore, in the present embodiment, the previous color misregistration correction process is executed at the start of printing, the previous color misregistration correction process is performed based on the number of prints of the previous print process, and the elapsed time from the previous print process. The process is executed when the number of printed sheets exceeds a certain number and a predetermined time has elapsed. Since the other parts including the hardware configuration are configured in the same manner as in the first embodiment described above, redundant description is omitted.

  The control procedure of the present embodiment is obtained by inserting the processing steps of Steps C1 to C5 between Steps B3 and B4 in the flowchart of FIG. 4 and transforming the processing of Steps B7 and B14 into Steps B7 ′ and B14 ′. . Only different points will be described below.

  In the flowchart of FIG. 9, the elapsed time from the previous print end time is measured in step B3. In the time measurement, the time measurement counter inside the time measurement unit 104 is cleared in step B16 and the count is started, so that the elapsed time can be calculated by reading the counter value in step B3. In step C1, it is compared whether the elapsed time from the previous printing end time is greater than a preset set value ΔT. If it is smaller than ΔT, it is determined that the change from the previous printing is small, and the color misregistration correction processing is performed. Without performing this, P1 counting the current printing process is cleared to 0 in step C5.

  If it is larger than the set value ΔT, in step C2, the number of printed sheets P1 at the previous printing is compared with a preset value P3. If the number of sheets at the time of the previous printing is large, a large amount of printing is continuously performed, so there is a high possibility that the temperature of the device has risen. For this reason, when the color misregistration correction is performed during this period, the color misregistration is corrected in a state where the temperature has risen, and thus the color misregistration correction is corrected to a state far from the initial state. Therefore, if the elapsed time from the previous printing end time is long and the number of sheets at the time of the previous printing is large, there is a possibility that the color misregistration will become large if printing is performed as a result of the color misalignment adjustment at the previous printing. In step C3, color misregistration correction is executed, and the number of printed sheets P since the previous color misregistration correction is cleared to zero. In steps B7 'and B14', the number of printed sheets P since the previous color misregistration correction is cleared to zero. Other processes are the same as those in the flowchart in the first embodiment shown in FIG.

  According to the present embodiment, in addition to the effects of the first embodiment, color misregistration during printing after being left can be reduced, so that the color misregistration amount can always be controlled within a certain range. it can.

<Third Embodiment>
In this embodiment, the image forming apparatus according to the first or second embodiment is applied to a direct transfer type printer, and only the detection position of the toner mark sensor 108 is different from the example of FIG. In other words, the toner mark sensor 108 is provided on the lower surface side of the transfer belt 51 in the figure on the fixing side (downstream side in the paper conveyance direction). When correcting the color misregistration, the recording paper is not passed, and the toner patterns 11-1 and 11-2 for misregistration detection shown in FIG. 14 are output on the transfer belt 51, and the patterns 11-1 and 11-2 are output. Is detected by the toner mark sensor 108, and the deviation amount of each color from the normal position is detected from the detection result. For the detected deviation amount, an optimum correction amount is calculated by following the processing procedure described in the first or second embodiment, and the writing amount and magnification in the main scanning and sub-scanning directions are calculated using the correction amount. Color misregistration correction processing is performed by adjusting the set value.

  Other parts that are not particularly described are configured in the same way as the first or second embodiment described above or the conventional example shown in FIG.

  According to the present embodiment, the effects of the first and second embodiments can be obtained by a direct transfer tandem color printer.

<Fourth Embodiment>
In this embodiment, the image forming apparatus according to the first or second embodiment is applied to an indirect transfer type printer. The toner mark sensor 108 is provided on the lower surface side of the transfer belt 51 in the figure on the secondary transfer roller 54 side (downstream side in the paper conveyance direction). At the time of color misregistration correction, the recording paper is not passed, and the toner pattern for misregistration detection shown in FIG. 3 is output on the transfer belt 51, and this pattern is detected by the toner mark sensor 108. The amount of deviation from the normal position of each color is detected. For the detected deviation amount, an optimum correction amount is calculated according to the processing procedure described in the first or second embodiment, and the writing amount and magnification in the main scanning and sub-scanning directions are calculated using the correction amount. Color misregistration correction processing is performed by adjusting the set value.

  Other parts not specifically described are configured in the same manner as the first or second embodiment described above or the conventional example shown in FIG. 13 and function in the same manner.

  According to the present embodiment, the effects of the first and second embodiments can be obtained with an indirect transfer tandem color printer.

1 is a block diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. 1 is a diagram illustrating a schematic configuration of a plotter unit of an image forming apparatus according to a first embodiment of the present invention. It is a flowchart which shows the process sequence of the color shift correction process in the 1st Embodiment of this invention. It is a flowchart which shows the process sequence including the correction process which considered the number of printed sheets and printing time in the 1st Embodiment of this invention. FIG. 6 is a diagram illustrating a change in environmental temperature using a time of the image forming apparatus during printing and when left as a parameter as a parameter. It is a figure which shows the correction coefficient tabulated of the number of printed sheets which considered the environmental temperature change of FIG. FIG. 10 is a diagram illustrating another example of an environmental temperature change using the time of the image forming apparatus during printing and when left as a parameter. It is a figure which shows the correction coefficient tabulated of the number of printed sheets which considered the environmental temperature change of FIG. It is a flowchart which shows the process sequence including the correction process which considered the number of printed sheets and printing time in the 2nd Embodiment of this invention. It is a figure which shows schematic structure of the printer of the direct transfer system which concerns on the 3rd Embodiment of this invention. It is a figure which shows schematic structure of the printer of the indirect transfer system which concerns on the 4th Embodiment of this invention. It is a figure which shows schematic structure of the printer of the direct transfer system currently implemented. It is a figure which shows schematic structure of the printer of the indirect transfer system currently implemented conventionally. It is a figure which shows the example of the pattern for color misregistration amount detection implemented conventionally.

Explanation of symbols

1K, 1M, 1C, 1Y Writing unit 2K, 2M, 2C, 2Y Photosensitive drum 3K, 3M, 3C, 3Y Developer 4K, 4M, 4C, 4Y Transfer device 7 Plotter controller 11-1, 11-2 Pattern 51 Transfer belt 70 recording paper,
100 CPU
101 ROM
102 RAM
103 Parameter memory 106 Plotter 108 Toner mark sensor 109 Temperature detection sensor

Claims (6)

A toner pattern for detecting the color misregistration amount is output on the belt, the position of the toner pattern is detected, the color misregistration amount is calculated from the detected toner pattern position information, and the color misregistration amount is minimized. In the color misregistration correction method to be corrected,
Measuring the time interval from the end of the previous print to the start of this print ,
Executed after the measuring step and determining whether a large amount of printing is continuously performed;
Setting an execution condition for executing the next color misregistration correction according to the measured execution interval;
A step of comparing the number of printed sheets obtained based on the set execution condition with a predetermined number of sheets;
Executing color misregistration correction processing when the number of printed sheets is larger than the predetermined number in the comparing step;
Equipped with a,
A color misregistration correction method characterized by executing the step of setting the execution condition after performing the color misregistration correction when it is determined in the determining step that a large amount of printing is continuously performed . A means for outputting a toner pattern for detecting a color misregistration amount on the belt, a means for detecting the position of the toner pattern, and calculating the color misregistration amount from the detected toner pattern position information, so that the color misregistration amount is minimized. And an image forming apparatus having a means for correcting so that
Means for measuring the time interval from the end of the previous print to the start of this print,
Means for determining whether a large amount of printing is performed continuously after the measuring step;
Means for setting an execution condition for executing the next color misregistration correction according to the measured execution interval;
Means for comparing the number of printed sheets obtained based on the set execution condition with a predetermined number of sheets;
Means for performing color misregistration correction processing when the number of printed sheets is greater than the predetermined number as a result of comparison by the comparing means;
With
An image forming apparatus according to claim 1, wherein when the determination unit is continuously printing a large amount, the execution condition is set after performing the color misregistration correction . The setting means, when calculating the number of printed sheets from the previous color misregistration correction, multiplies the number of printed sheets by a constant coefficient according to the interval until the next printing. The image forming apparatus according to claim 2, wherein the execution condition is set to be smaller than the actual number of printed sheets . Further comprising means for measuring the ambient temperature,
The setting means changes a coefficient indicating the color shift change due to the standing time according to the measured environmental temperature, and executes the next color shift correction using an optimum correction coefficient according to the coefficient change. The image forming apparatus according to claim 2, wherein execution conditions are set. The image forming apparatus according to claim 2, wherein the belt is a conveyance belt that conveys a sheet onto which an image is directly transferred . The belt, an image is primarily transferred, according to any one of claims 2 to 4, characterized in that an intermediate transfer belt for transferring the transferred image onto the paper at the secondary transfer position Image forming apparatus.

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